The current use of particle-based packed chromatography columns involves packing particles dissolved in a slurry into a tube and then burning fits on either end of the packed tube to retain the packed bed in the tube. This procedure is more of an art than a science and requires skilled personnel to pack the tubes and burn the fits. Thus, manually packed particle-based chromatography columns have significant person-to-person reproducibility issues.
In addition, particle-based packed columns for use in capillary electrochromatography (CEC) are time consuming to fabricate, fragile, and tend to have bubble formation. The bubble formation causes irreproducible retention times and peak areas, therefore making particle-based packed columns impractical to use for the analysis of real world samples.
Polymeric monolithic stationary phases offer an alternative to the classical microparticulate sorbents and provide certain advantages for sample analysis. In contrast to the traditional packed particle stationary phases, monolithic separation media are made of a continuous, rigid polymeric rod with a porous structure. The lack of intraparticular void volume improves mass transfer and separation efficiency, allowing for fast, high-quality separations.
For almost a decade, CEC using monolithic columns has been a growing field of research as an alternative to the traditional packed column CEC. The main advantages of monolithic columns for CEC are: the uncomplicated procedures for column preparation, the flexibility in tuning the columns' pore structure, the elimination of the need for frits, the availability of various functional monomers in the columns for selective separation, and the exclusion or reduction of bubble formation during operation. Hence, use of monolithic column technology has increased and new stationary phases and column-preparation mechanisms are being researched. Furthermore, a large number of new and attractive applications have been developed in biological, environmental, and pharmaceutical analysis which may benefit from using monolithic column technology.
The stationary phase used for CEC plays a dual role of providing sites for the desired interaction with analytes and sites for generating electroosmotic flow (EOF). For instance, in the preparation of a methacrylate-based monolith used for CEC, a charge-bearing monomer, such as 2-acrylamido-2-methyl-1-propanesulfonic acid, is often used to provide stable EOF in addition to use of a functional monomer. There is a need for monolithic columns that are chargeable and thus suitable for CEC. There is furthermore a need for monolithic chromatography columns with enhanced electro-osmotic flow.
The advantages of capillary high performance liquid chromatography (HPLC) over conventional normal scale HPLC also have been recognized. Those advantages include increased chromatographic resolution, lower sample consumption, the ability to analyze and isolate rare compounds of interest, reduced solvent consumption and convenient on-line connection to electrospray mass spectrometry.
It would be desirable to provide additional monolithic columns for chromatography, such ac CEC and HPLC, which reduce or avoid one or more the aforementioned deficiencies.